"The lungs start to fill up with water," said Dr. Profeta. "It's not necessarily the water they've inhaled, but it's a biological, physiological response to near-drowning."

Simply put, secondary drowning happens when you breathe in water instead of swallowing water.

"If you've had a child that's had a near-drowning episode, I would certainly hope that you'd bring them into the emergency department, but if they look fine and you're at home and all of a sudden the child takes a turn for the worse, starts coughing a lot, complaining of having trouble breathing, you need to bring them immediately to the emergency department."

Dr. Profeta says it typically happens about seven hours later, but it has happened as quickly as a couple hours. Within 24 to 48 hours, you're in the clear.

Secondary drowning is survivable if you get help at the first sight of the warning signs.

"Coughing, difficulty breathing, breathing fast, listless, they look sick, they look like a bad asthma attack or any other respiratory illness."

Sudden mood swings are another sign.

Dr. Profeta says to trust your gut more than anything.

This is rare, but if it happens, it is deadly if you don't act immediately.